A Versatile Illumination System for Real-Time Terahertz Imaging

Abstract

Terahertz technologies are attracting strong interest from high-end industrial fields, and particularly for non-destructive-testing purposes. Currently lacking compactness, integrability as well as adaptability for those implementations, the development and commercialisation of more efficient sources and detectors progressively ensure the transition toward applicative implementations, especially for real-time full-field imaging. In this work, a flexible illumination system, based on fast beam steering has been developed and characterized. Its primary goal is to suppress interferences induced by the coherence length of certain terahertz sources, spoiling terahertz images. The second goal is to ensure an enhanced signal-to-noise ratio on the detector side by the full use and optimized distribution of the available power. This system provides a homogeneous and adjustable illumination through a simplified setup to guarantee optimum real-time imaging capabilities, tailored to the sample under inspection. Working toward industrial implementations, different illumination process are conveniently assessed as a result of the versatility of this method.

Advanced Data Processing For Tomography and 3D Rendering With Terahertz Waves

“…In this work, we employed a Lytid's teracascade 1000 QCL source. In order to overcome the limiting artifacts induced by the high coherence of such THz QCL sources, and ensure the versatility of the imaging system, the homogeneous illumination in the object plane is performed via a combination of fast beam steering centering purposes, as well [3]. For tomography experiment, the sample is positioned onto a rotation stage and acquisitions were performed in real time.…”

Single-scan multiplane phase retrieval with a radiation of terahertz quantum cascade laser

“…In this work, Lytid's TeraCascade 1000 QCL source, with an emission power of 1.3 mW at 2.5 THz, has been employed in combination with its integrated autoalignment unit ('AAU' in Fig. 1) to provide a collimated illumination beam through 1" optics [2,60].…”

“…The increasing interest in the terahertz (THz) frequency range in recent decades has given rise to a new branch of techniques and algorithms for the non-contact evaluation of surface and subsurface features of various samples and materials. In this field, THz imaging [1][2][3] represents one of the most promising approaches, since it provides spatially resolved information about the investigated objects. THz phase imaging (THz PI) [4,5], which includes pulse time-domain holography (PTDH) [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] as well as continuous wave (CW) holography [23][24][25][26][27][28][29][30], Hartmann wavefront sensing [31][32][33][34][35], shearorgaphy [36], ptychography [37][38][39][40][41], and other phase retrieval techniques [42][43][44][45]...…”

Segmentation of THz holograms for homogenous illumination

“…Homogeneous illumination is one of the wide range of beam shaping challenges. It generally finds application in laboratory tasks requiring full sample area analysis 1 , industrial irradiation 2 , or imaging 3 . In the terahertz (THz) range, it can be applied for specific tasks of sample illumination, e.g., for skin cancer detection 4 or nondestructive testing 5 .…”

“…Uniform illumination can be obtained with either passive or active approaches. The latter usually focuses on scrambling phase distribution or scanning the sample areas with, e.g., a swiveling mirror 3 , 7 , which implies the addition of moving elements into a setup. Depending on an application, mechanical vibrations from moving elements and total scrambling of the phase of the wavefront might be undesirable.…”